1. Field of the Invention
The present invention relates to a bonding apparatus, and more particularly, to a bonding apparatus and system for fabricating a liquid crystal display device.
2. Background of the Related Art
As demands on display devices increases, various flat display panel device, such as liquid crystal display (LCD), plasma display panel (PDP), ELD electro-luminescent display (ELD), and vacuum fluorescent display (VFD) devices have been proposed. The LCD devices have been commonly used as mobile displays to replace cathode ray tube (CRT) devices because of their excellent picture quality, light weight, thin profile, and low power consumption. In addition, mobile type LCDs, such as monitors for notebook computers, are being developed for televisions to receive and display broadcasting signals, and as monitors of computers.
Despite various technical developments for the LCD devices, efforts for enhancing picture quality of the LCD devices have been inconsistent. Accordingly, in order for the LCD devices to be deployed as a general use display device, the LCD devices must have high picture quality, i.e., high definition and luminance, and must be of a large size while maintaining the features of light weight, thin profile, and low power consumption.
LCD devices may be fabricated by an LCD injection method, in which one substrate having a sealant pattern formed thereon, which includes an injection hole, is bonded to the other substrate under a vacuum, and liquid crystal material is injected therein through the injection hole. Alternatively, the LCD devices may be fabricated using a liquid crystal dropping method, as disclosed in Japanese Patent Publication Nos. H11-089612, and H11-172903, in which one substrate having liquid crystal dropped thereon and the other substrate are provided, and the two substrates, placed opposite along a vertical direction, are bonded together. Of the two methods, the liquid crystal dropping method is advantageous in that different components can be dispensed directly onto the substrate surface.
FIG. 1 is a cross sectional view of a liquid crystal display bonding apparatus during a loading procedure according to the related art. In FIG. 1, the bonding apparatus is provided with a frame 10 forming an outer shape, an upper stage 21, a lower stage 22, a sealant outlet part (not shown), a liquid crystal dropping part 30, upper chamber part 31, lower chamber part 32, a chamber moving system 40, and a stage moving system 64. The sealant outlet part (not shown) and the liquid crystal dropping part 30 are attached to a side of the frame 10, and the upper and lower chamber parts 31 and 32 are detachable from each other.
The chamber moving system 40 includes a driving motor for selectively moving the lower chamber part 32 to a location during a bonding procedure, or to a location where discharge of the sealant and dropping of the liquid crystal material are performed.
The stage moving system 64 is provided with a motor, shafts 61, a housing 62, a linear guide 63, a ball screw 65, and a nut housing 66. The upper stage 21 is held by the shafts 61 that are attached to the housing 66. The housing 66 is attached to the frame 67 with a linear guide, and the motor 64 is attached to a bracket 68 on the frame 67 for driving the nut housing 66 along upward and downward directions. Driving power is transmitted by the ball screw 65 and the nut housing 66, which is connected to the housing 66 through a load cell 69.
Process steps for fabricating an LCD using the bonding apparatus according to the related art will now be explained. Initially, an upper substrate 51 is loaded on the upper stage 21, and a lower substrate 52 is loaded onto the lower stage 22. Accordingly, as shown in FIG. 1, the lower chamber part 32 having the lower stage 22 is moved to a location for sealant coating and liquid crystal dropping by the chamber moving system 40.
Next, as shown in FIG. 2, when the sealant coating and the liquid crystal dropping are finished by the sealant outlet part (not shown) and the liquid crystal dropping part 30, the lower chamber unit 32 is moved to a location for bonding the upper and lower substrates 51 and 52 by the chamber moving system 40. Then, the upper and lower chamber units 31 and 32 are aligned by the chamber moving system 40, and the upper and lower chamber parts 31 and 32 are attached together to form a closed chamber. Next, pressure within the closed chamber is reduced using a vacuum system to create a vacuum state within the closed chamber. Then, the shaft 61 is moved along the downward direction by the motor 64, thereby moving the upper stage 21 to bond the upper and lower substrates 51 and 52 together. The load cell 69 functions as a pressure sensor for controlling the motor 64 with reference to a load signal generated by the load cell 69. Accordingly, an amount of bonding pressure may be controlled at a preset value.
However, the bonding apparatus according to the related art has the following problems. First, a positional variation of the system for moving the upper stage 21 along the upward and downward directions is created after a repeated period of use. Accordingly, an error due to the flatness of the upper stage is created. In addition, since the drive shafts 65 of the stage moving system receive driving forces from the driving motor 64 to move the upper stage 21 along the downward direction with a precise force, an accurate flatness setting of the upper stage 21 has been difficult to achieve prior to initial processing.
Second, wear at particular parts of the upper stage 21 may cause defective bonding at particular parts of the upper and lower substrates 51 and 52. Accordingly, when a height difference along a lower surface of the upper stage 21 is created, bonding of the upper and lower substrates 51 and 52 is defective. For example, as shown in FIG. 3, during bonding of the upper and lower substrates 51 and 52, dispersion of the spread of the liquid crystal material LC is not adequate. Accordingly, a gap S is formed between adjacent sealant parts, thereby preventing equal dispersion of the liquid crystal material LC. For example, when a portion of the lower substrate 52 has the liquid crystal material LC dropped thereon is higher than a portion where the sealant is coated, the load cell 69 (in FIGS. 1 and 2) reads that bonding of the upper and lower substrates 51 and 52 is completed even if the portion having the sealant coated thereon is not adequately pressed. Thus, without adequate pressing of the sealant, the portion of the seal breaks. The broken seal results in improper bonding of the upper and lower substrates 51 and 52, and allows ambient air to infiltrate into the device.